Photovoltaic (PV) or solar cells are material junction devices which convert sunlight into direct current (DC) electrical power. When exposed to sunlight, the electric field of solar cell p-n junctions separates pairs of free electrons and holes, thus generating a photo-voltage. A circuit from n-side to p-side allows the flow of electrons when the solar cell is connected to an electrical load, while the area and other parameters of the PV cell junction device determine the available current. Electrical power is the product of the voltage times the current generated as the electrons and holes recombine.
Thin-film solar devices typically include multiple thin layers of material deposited on sheet glass, and are typically subdivided into a large number (between 100 and 200) of individual solar cells by scribing processes that also define the electrical interconnects for adjacent cells, which are electrically connected in series to produce power with a current. Laser scribing enables high-volume production of next-generation thin-film devices, and laser scribing out performs mechanical scribing methods in quality, speed, and reliability.
The laser-material interaction involves complex processes of heating, melting, vaporization, ejection of atoms, ions and molecules, shock waves, plasma initiation and plasma expansion. The resulting crater and laser-induced plasma are dependent on the laser beam parameters (e.g., duration, energy, and wavelength), the solid target properties, the surrounding environment's conditions, and, if passing through the superstrate, the condition and composition of the substrate (e.g., glass). For example, debris on the exposed surface of the superstrate (i.e., opposite from the thin film stack) can greatly affect the quality of the scribe line formed in the thin film stack, which can lead to shunting and other issues. Such issues can, in turn, lead to variations in performance of the resulting PV module.
As such, a need exists for more precisely laser scribing multiple thin films on a glass superstrate, especially cadmium telluride based thin film photovoltaic devices.